this table contain id ==>employee id & vacdate ==> is the start date of vacation of the employees && vacinterv ===> the time interval of the vacation for example 7 means 7 days from 13-oct-13 until 20-oct-13

the problem is there are employees (i.e id 10) take overlapping vacation [take 25-jan-13 (interval 6 ) until 21-jan-13] but by mistake take 27-jan-13 other vacation which cause vacation overlapping
How can i select the employees who have overlapping vacation?